Surface reflection is a phenomenon that occurs due to the refractive index difference between air and surfaces. It is one of the major limiting factors of light absorption efficiency in photovoltaic and optoelectronic devices. Consequently, there has been considerable interest in light trapping management of various semiconductor material surfaces. For example, coating of antireflection (or antireflective) (AR) layers on semiconductors has been shown to reduce surface reflections, but the coatings may be effective for only certain optical bandwidths and over a limited angular range. Direct formation of AR microstructures on semiconductor surfaces using reactive ion etching (RIE) has been explored to address the shortcomings of traditional AR coatings, but RIE can induce damage that diminishes device performance.
Photodetectors are optoelectronic devices employed for light sensing across various wavelength ranges—e.g., from infrared (IR) to ultraviolet (UV). Detection of longer wavelengths, such as near-infrared (NIR) wavelengths, is important for various applications, including optical fiber communications, remote sensing of the environment, monitoring of industrial processes and pollution, automotive security, biology and medicine. Shorter wavelength UV detectors are of interest due to potential applications in air purification, flame detection, and missile guidance, among others. In many UV detection applications, it is highly desirable to detect UV light without sensing visible or IR light, or solar UV wavelengths longer than 280 nm that can penetrate the Earth's atmosphere. Thus, UV detectors with a cut-off below 280 nm are sought after. Such “solar-blind” photodetectors ideally respond only to UV radiation with wavelengths shorter than the solar radiation that reaches the Earth and produce no measurable signal when exposed to normal outdoor lighting.